1. Field of the Invention
The invention generally relates to solenoid-operated valves for use in internal combustion engines, and particularly relates to technologies for starting the solenoid-operated valves in favorable manners.
2. Description of Related Art
Solenoid-operated valves for an internal combustion engine installed on a vehicle, such as an automobile, are known which are operable to drive intake valves and/or exhaust valves for opening and closing the same by utilizing electromagnetic force. Each of the solenoid-operated valves includes an armature that moves along with a valve body of an intake valve or an exhaust valve, a valve-opening spring that urges the armature in a direction to open the valve, a valve-closing spring that urges the armature in a direction to close the valve, a valve-opening electromagnet that generates electromagnetic force for opening the valve against the bias force of the valve-closing spring, and a valve-closing electromagnet that generates electromagnetic force for closing the valve against the valve-opening spring.
When the solenoid-operated valve is not actuated, namely, when no exciting current is applied to the valve-opening electromagnet and the valve-closing electromagnet, the armature is resiliently supported at a neutral position at which the bias forces of the valve-opening spring and the valve-closing spring are balanced with each other.
Since the valve body is half-open when the armature is located at the neutral position, the armature needs to be moved to its opening-side terminal position at which the valve body is fully open, or to its closing-side terminal position at which the valve body is fully closed, when the internal combustion engine is started, for example.
One example of a method of moving the armature to the opening-side terminal position or the closing-side terminal position at the time of a start of the engine, or the like, is disclosed in, for example, Japanese Laid-open Patent Publication No. 2000-97059. In this publication, it is proposed to move armatures of a plurality of solenoid-operated valves from the neutral position to the opening-side terminal position upon turn-on of an ignition switch, hold the armatures at the opening-side terminal position, and successively move the armatures to the closing-side terminal position in a predetermined order in which the cylinders of the engine enter the intake stroke after the speed of rotation of the crankshaft reaches a reference value.
In the method described in the above-identified publication, all of the intake and exhaust valves are moved from the neutral position to the fully open position at the time of a start of the engine. Subsequently, all of the intake and exhaust valves are held at the fully open position until the speed of rotation of the crankshaft reaches the reference value. Consequently, compression work to be done by the engine during cranking is reduced, and the starting period of the engine and the amount of electric power consumed by a starter motor can be reduced.
While all of the intake and exhaust valves are moved from the neutral position to the fully open position upon a start of the engine according to the known technology as described above, all of the intake and exhaust valves are not necessarily likely to reach the fully open position.
When the intake valve or exhaust valve that is likely to reach the fully closed position is moved to the fully open position, the amount of electric power consumed by the valve-opening electromagnet and/or valve-closing electromagnet is increased, or the armature may not successively displace from the neutral position to the opening-side terminal position. Consequently, it becomes difficult to appropriately start the internal combustion engine. This problem also occurs when all of the intake and exhaust valves are moved to the fully closed position at the time of a start of the engine.